Detection of microsatellite
variation by capillary gel electrophoresis
Microsatellite variation is detected by a combination of PCR amplification and electrophoretic separation. Once a microsatellite locus is identified, two PCR priming sites with unique DNA sequences are identified on either side of the repeat region [top]. PCR amplification generates a DNA fragment of a particular size [middle], depending on the number of repeats in the microsatellite locus present. The size of the allele can be measured by the use of DNA size markers run simultaneously with the PCR product [bottom].
In the left-hand example, the individual tested is homozygous and only a single allele is present, which is detected as a single fragment 184bp long. In the right-hand example, the individual is heterozygous for two alleles, which are both amplified by the same PCR primers and are detected as two fragments of 184bp and 188bp.
Figure © 2012 TA Brown, Introduction to Genetics (1st ed.); additional text © 2012 by Steven M. Carr